Stoke host Chelsea tomorrow and Hughes thinks they are struggling to master the dark arts this season.
"I think they've got more sendings off in the opening five or six games as in the whole of last year," he said.
"So is it an anomaly or a disciplinary issue? I think last year they were good at taking things up to a line and not crossing it and maybe they have (this season) just got that wrong.
"If you look at Costa, he was brilliant at taking it up to the edge, then stepping back, and it affected opposition teams.
"Maybe they haven't quite got that ability in terms of getting the dark arts right on spec."